8.7. Equalize

The Equalize
command automatically adjusts the brightness of colors across the active
layer so that the histogram for the Value channel is as nearly flat as
possible, that is, so that each possible brightness value appears at about
the same number of pixels as every other value. You can see this in the
histograms in the example below, in that pixel colors which occur
frequently in the image are stretched further apart than pixel colors
which occur only rarely. The results of this command can vary quite a bit.
Sometimes “Equalize”
works very well to enhance the contrast in an image, bringing out details
which were hard to see before. Other times, the results look very bad. It
is a very powerful operation and it is worth trying to see if it will
improve your image. It works on layers from RGB and Grayscale images. If
the image is Indexed, the menu entry is insensitive and grayed out.

8.7.1. Activate the Command

You can access this command from the image menubar through
Colors → Auto → Equalize

or by using the keyboard shortcut
Shift+Page Down.

8.7.2. “Equalize” example

Figur 16.135. Original image

The active layer and its Red, Green, Blue histograms before
“Equalize”.